An integral part of functionally testing modern technical equipment is verifying, or certifying, that the test instruments used to make the functional tests operate properly and within their rated accuracy. Test instruments used to generate stimuli to equipment under test must be certified to ensure that the desired stimuli are, in fact, produced. Test instruments used to measure the response of equipment under test must be certified to ensure that equipment responses are accurately quantified or qualified. If either type of test instrument fails to function properly, the functional testing process in which the instruments are used may be faulty. The functional testing could produce test results indicating that a portion of some equipment is malfunctioning, when in fact, it is not, or alternatively indicating that a portion of the equipment operates properly when the opposite is true.
A process related to instrument certification is calibration. Calibration is the process of adjusting components on test instruments so that the instruments either deliver appropriate stimuli or make accurate measurements, and/or determining appropriate corrections to be applied to the instruments. Certification and calibration are usually performed together as an iterative process. If an instrument fails a certification test, it is calibrated. The instrument is then subjected to another certification test. In this manner, an instrument is repeatedly subjected to certification testing and calibrated until it either passes certification or is deemed unusable.
Calibrating and certifying the instruments used to functionally test aircraft and other complex equipment is a difficult task. An aircraft, for example, comprises a number of different systems, each of which is designed to perform a general function. Each system is usually made up of separate subsystems comprising numerous components designed to perform a specific task. Manufacturing, maintenance, safety, and regulatory requirements demand that the individual components and subsystems be subject to frequent and extensive functional testing. Functional testing of this nature requires a large number of, and different types of, test instruments. Each test instrument must be subjected to a specific calibration and certification process for each function the instrument performs to ensure that the instrument operates properly. Significant amounts of technician time are thus required to perform the individual calibration and certification processes. Moreover, the certification tests and calibrating adjustments performed on any individual instrument are inherently subject to technician error. The number of certification and calibration processes that must be performed on large numbers of test instruments used in some environments increases the likelihood that even the most conscientious technician may improperly calibrate and certify a given instrument.
In addition, one type of test instrument can have different certification requirements that depend on the specific system the instrument is used to test. An instrument may be calibrated and certified for test functions that are not involved in the particular functional testing for which the instrument will be used. At the least, this type of calibration and certification may simply result in excess time being spent certifying the instrument. At the worst, this type of calibration and certification can result in a test instrument being certified as operational when, in fact, it may not be so certified for the tests it is used to perform.
Instrument calibration and certification also requires that each time a test instrument is calibrated and certified, a record of the processes be made. Calibration and certification records are used for studying fault histories of the instruments so that the source of the faults can be identified and corrected. Calibration and certification records are also used for determining if a particular instrument has a fault pattern that indicates that the accuracy of the instrument for functional testing cannot be guaranteed. Regulatory authorities often require instrument certification records to be maintained so that the authorities can verify that only properly certified test instruments are used for functional testing.
Generating and maintaining instrument calibration and certification records contributes to the complexities of the calibration and certification processes. The time required to maintain a "paper trail" of each certification test adds to the time required to calibrate and certify each instrument. Human error can cause the results of any certification test to be either inaccurately entered or inaccurately transcribed.